Qualitative Analysis (Detection of Nitrogen, Sulphur, Phosphorus, and Halogens ) NEET Questions

Organic Chemistry - Purification and Characterization of Organic Compounds

Qualitative Analysis (Detection of Nitrogen, Sulphur, Phosphorus, and Halogens ) MCQ Questions


13.
Why is acetic acid (and not sulphuric acid) used to acidify the sodium fusion extract while testing for sulphur using lead acetate?
A.
Because acetic acid increases the solubility of PbS
B.
Because acetic acid is a stronger acid
C.
Because sulphuric acid does not dissolve lead salts
D.
Because sulphuric acid would react with lead acetate to give white PbSO₄, masking/interfering with the test
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ANSWER :
D. Because sulphuric acid would react with lead acetate to give white PbSO₄, masking/interfering with the test
14.
The chemical species responsible for the violet colour in the sodium nitroprusside test for sulphur is:
A.
[Fe(CN)₆]⁴⁻
B.
[Fe(CN)₅NOS]⁴⁻
C.
PbS
D.
Fe₂S₃
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ANSWER :
B. [Fe(CN)₅NOS]⁴⁻
15.
When both nitrogen and sulphur are present in an organic compound and limited sodium is used in fusion, the species formed in the sodium fusion extract is:
A.
NaCN and Na₂S separately
B.
NaSCN (sodium thiocyanate)
C.
NaCNO (sodium cyanate)
D.
NaNO₂
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ANSWER :
B. NaSCN (sodium thiocyanate)
16.
When NaSCN reacts with Fe³⁺ in solution (when both N and S are present in the organic compound), the colour observed is:
A.
Prussian blue
B.
Black
C.
Blood red
D.
Violet
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ANSWER :
C. Blood red
17.
If excess sodium is used during fusion of an organic compound containing both N and S, the test will give:
A.
Both Prussian blue (for N) and black PbS (for S) tests
B.
No colour at all
C.
Only blood red colour
D.
Only violet colour
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ANSWER :
A. Both Prussian blue (for N) and black PbS (for S) tests
18.
In the test for halogens, the sodium fusion extract is acidified with which acid before adding silver nitrate?
A.
Acetic acid
B.
Dilute HCl
C.
Dilute H₂SO₄
D.
Dilute HNO₃
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ANSWER :
D. Dilute HNO₃